Apparatus for continuous casting of hollow bar

ABSTRACT

Apparatus for casting a hollow bar which includes a mold having a mandrel therein and means for distributing molten material to the mold inlet in an area between the mold and the mandrel. Initially a starting plug closes the mold outlet to prevent leakage of the molten material and provides means to join the plug and solidified melt. After the molten material freezes in the annulus around the mandrel, the starting plug is lowered at a controlled rate to draw the solidified hollow bar from the mold outlet as additional molten material is fed through the inlet. An air inlet into the hollow of the cast bar prevents the formation of a vacuum within the hollow. Further, means are provided for cooling the mold to quickly freeze the molten material as it is fed into the mold.

United States Patent Fabens, Jr.

1 1 July 25, 1972 [54] APPARATUS FOR CONTINUOUS CASTING OF HOLLOW BAR [72] Inventor: Andrew Lawrie Fabens, Jr., Shaker l-lts.,

Ohio

[73] Assignee: Truline Casting Company, Wickliffe, Ohio [22] Filed: Nov. 3, 1971 [21] Appl. No.: 195,649

Related U.S. Application Data [63] Continuation-impart of Ser. No. 5,694,;lan. 26, 1970,

abandoned.

[52] U.S. Cl ..164/274, 164/85, 164/281 [51] Int. Cl ..B22d 11/08 [58] Field of Search 164/73, 82, 85, 89, 268, 274, 164/281 [56] References Cited 1 UNITED STATES PATENTS 2,747,244 5/1956 Goss ..164/73 UX 3,331,430 7/1967 Earl, Jr. ..,.l64/85 X 3,342,252 9/1967 Wood et al.. ....164/73 X 3,481,391 12/1969 Nowak ..164/85 X FOREIGN PATENTS OR APPLICATIONS 833,393 3/1952 Germany ..l64/82 OTHER PUBLICATIONS A.P.C. Application of Roth et al., Ser. No. 162,538, published April 27, 1943.

Primary Examiner-R. Spencer Annear Attorney-Robert .l. Fay et al.

[57] ABSTRACT Apparatus for casting a hollow bar which includes a mold having a mandrel therein and means for distributing molten material to the mold inlet in an area between the mold and the mandrel. Initially a starting plug closes the mold outlet to prevent leakage of the molten material and provides'means to join the plug and solidified melt. After the molten material freezes in the annulus around the mandrel, the starting plug is lowered at a controlled rate to draw the solidified hollow bar from the mold outlet as additional molten material is fed through the inlet. An air inlet into the hollow of the cast bar prevents the formation of a vacuum within the hollow.

freeze the molten material as it is fed into the mold.

28 Claims, 9 Drawing Figures I Patented July 25, 1972 3,678,990

3 Sheets-Sheet 1 INVENTOR. F i G. 4

BY 1 1 m}, 5W )3 Mulolhnd ATTORNEYS A. LAWRIE FABENS,JR.

Patented Jilly 25, 1972 3 Sheets-Sheet 2 \W .H H....... M. E 7 4 J//// 6 4 FIG. 3

INVENTOR. A. LAWRIE FABENS,JR

BY 4W 5 &' MM

ATTORNEYS APPARATUS FOR CONTINUOUS CASTING OF HOLLOW BAR This is a continuation-in-part of my copending application, Ser. No. 5,694, filed Jan. 26, 1970, entitled Method and Apparatus for Continuous Casting of Hollow Bar, now abandoned. I

BACKGROUND OF THE INVENTION Conventional apparatus for continuously casting a bar includes a mold fed with molten material from a tundish. Initially the mold outlet is blocked by a plug supported on a starting bar to prevent the escape of molten material. After a small amount of molten material is fed into the mold and has solidified, the starting bar is lowered at a controlled rate. The solidified material leaves the mold supported on the plug as additional molten material is fed into the mold inlet. Substantially the same method and apparatus are used for solid bars and hollow bars; the only addition with hollow bars is an appropriately located mandrel supported in the mold cavity.

Usually such method and apparatus are employed with easy to cast alloys which have good initial strength upon solidification such as for example, copper or iron base alloys. Because of increased labor and machine tool costs, there is a need for a method and apparatus for casting hollow bars of hot short" alloys having properties which do not lend themselves to present casting processes. They lack the ability to withstand the substantial stresses due to thermal contraction while cooling through the brittle or hot short range. This property is fatal with the conventional processes of continuously casting hollow bars because the hollow is closed at both ends. The starting plug closes one end and the mandrel closes the other end. Thus, as the bar lengthens the hollow" increases in volume, thereby creating a vacuum within the hollow because there is no relief to maintain atmospheric pressure.

An additional problem exists at the start of the casting process, unless there is a firm connection between the starting plug and the solidified melt the plug will prematurely separate from the cast bar. Initially the solidified melt will have almost no weight projecting below the mold and thus it will not flow from the mold as a solidified bar by gravity alone. Unless the starting plug exerts a positive pulling force on the bar it will not exit from the mold.

The need in the industry is for an apparatus for continuously casting hollow bars of hot short alloys and this has led to the instant invention which is susceptible to use with hot short" alloys as well as those which have good early strength near molten temperatures.

BRIEF DESCRIPTION OF THE INVENTION A graphite liner is supported within a cooling metallic jacket to form the exterior casting surface of a mold. A spider bridges the inlet to the mold and supports an arbor which serves as a feeding and distributing device for molten material metered into the mold inlet. A graphite tip projects from the bottom of the arbor into the mold cavity to serve as a mandrel in the casting process.

At the beginning of the casting process a starting plug projects up into the mold near the bottom of the graphite tip and blocks the outlet to prevent leakage of molten material from the mold. Means are provided to lock the solidifying melt to the starting plug. The plug is attached to a starting bar extending downward from the plug through pinch rolls which control the casting rate, as will be explained subsequently. While pinch rolls are preferred in this invention, it is obvious that other conventional means for controlling the rate of withdrawal from the mold may be employed.

With the plug in place, molten material will be fed into the mold through the arbor and at such time as it solidifies against the plug, the pinch rolls will begin to turn slowly to lower the starting bar at a controlled rate. The solidified material within the mold forms an annulus around the mandrel which is the beginning of the hollow bar. The bar being cast to the plug is drawn from the mold by its controlled descent. Various means for locking the cast bar are employed to prevent premature separation.

Lubricant is continuously provided on the surface of the graphite liner to facilitate easy downward movement of the v cast bar while cooling means are provided about the metallic (preferably copper) jacket to quickly freeze the molten material in the mold.

A vent is provided, preventing a vacuum in the "hollow of the cast bar. During the casting of bars of hot short" alloys with conventional equipment, stresses due to contraction during cooling tend to cause cracks inthe bar along with other unpredictable imperfections. This problem is alleviated by avoiding a vacuum within the hollow as provided by this invention.

It is clear that the shape of the bar is optional. The periphery is controlled by the shape of the graphite liner and the shape of the hollow is controlled by the mandrel. Thus, any desired shape may be cast by supplying an appropriate liner and mandrel.

Objects of the invention will be obvious from a reading of the detailed description.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a fragmentary elevational view, partially in section, of the molding apparatus of this invention used in the casting of hollow bars.

FIG. 2 is a fragmentary elevational view of the molding apparatus of FIG. 1, in section, just prior to the start of the casting process.

FIG. 3 is a plan view of FIG. 2.

FIG. 4 is a fragmentary elevational view of a modification of the molding apparatus of FIG. 2, in section.

FIG. 5 is a fragmentary elevational view of another modification of the molding apparatus of FIG. 2, in section.

FIG. 6 is a fragmentary elevational view of the mold apparatus with a modified starting plug.

FIG. 7 is a fragmentary elevational view of the mold apparatus and includes a third modified starting plug.

FIG. 8 is a plan view ofthe plug of FIG. 7.

FIG. 9 is a sectional view of the plug taken along line 9-9 of FIG. 8.

PREFERRED EMBODIMENTS FIG. 1 illustrates the mechanism for feeding molten material into a mold which serves to cast hollow bars in a continuous process. It includes a furnace or ladle 10 having a spout 12 which pours molten material 14 into a tundish 16. An outlet 18 from the tundish serves as a gravity feed for the mold 20.

It is intended that there be a flow control of molten material from the tundish into the mold. Such control apparatus may include a needle control valve in the outlet 18 or other devices to provide uniform or controlled molten material feed. Such apparatus is well known in the art and for convenience is not illustrated in the drawing.

Molten material from the tundish I6 is fed into an arbor 22 supported by a spider 24 bridging the inlet of the mold 20. The arbor includes a central passage 26 communicating with radial passages 28 which serve to equally distribute the molten material at the mold inlet.

A graphite tip or mandrel 30 is affixed to the bottom of the arbor 22 by a bolt 32 which projects concentrically through a central opening 33 in the mandrel. The mandrel serves as the internal casting surface; the external casting surface is provided by a graphite liner 34 supported in a copper cooling jacket 36.

It is important that after the molten material solidifies it does not adhere to the liner 34. For this reason a lubricant is fed through a tube 38 to a vertical channel 40 in the jacket 36 which feeds circumferentially extending channels 42 in the liner 34. Because of the porous nature of graphite, the high temperature lubricating fluid will pass through the liner 34 and lubricate the casting surface allowing the cast hollow bar to be-drawn easily out of the mold. Under certain unique circumstances it might be possible to cast the bar without lubrication but the product is found to be much more uniform where lubricant is used.

It is intended that the cooling of the molten material be from the outside in, i.e., from the graphite liner 34 inward as indicated by the freeze line 44 of FIG. I This is accomplished by providing a cooling means for the jacket 36. Any desired cooling fluid may be used but water is preferred. The fluid is fed through an inlet pipe 46 into a heat exchanger 47 surrounding the jacket 36. A baffle 48 causes the water to flow upward from the inlet pipe 46 and then down at 49. The water exits from the exchanger at an outlet 50 where it impinges on the exterior surface of the solidified hot cast hollow bar. This second cooling of the bar by the water is the most efficient use of the cooling fluid and also helps to keep the other apparatus cool.

As is best seen in FIG. 2, at the start of the casting operation the starting plug 52 is attached to a starting bar 54 and projects up into the mold in close proximity to the bottom of the mandrel 30. An apertured pin 55 is affixed within the plug 52 by a set screw 56. The pin 55 and plug 52 serve as a unit and may be integral and serve as a plug combination. A groove 57 is formed in the pin 55 and when the molten metal solidifies, the resulting tongue-in-groove joint will lock the plug and cast bar together. The joint insures against separation of the bar and plug when the bar is drawn from the mold as will be explained subsequently.

Clearance between the pin 55 and the side walls of the cavity 58 in the bottom of the mandrel 30 should be kept to a minimum. An aperture 60 through to pin 55 must be kept open during the casting process; molten material could flow upward in the annulus around the pin and block the aperture 60 if the spacing is too wide.

When the molten material begins to solidify on the plug 52 it will fill the mold to an elevation substantially as shown at 61 in FIG. 1, at which time the pinch rolls 62 will begin to turn and lower the starting bar 54 at a controlled rate. As the starting bar lowers, air will pass through the aperture 60 in the'pin 55 to fill the cavity 64 within the formed hollow bar 66. As is obvious, without this venting or air feed mechanism a vacuum will be formed in the cavity 64 as the cast hollow bar 66 continues to descend and this is extremely detrimental with hot short" alloys. Until the hot short materials have been sufficiently cooled below the brittle range they are unable to .withstand the cooling stresses in combination with a differential pressure such as a vacuum within the hollow 64. The aperture 60 prevents the formation of a vacuum condition and allows the continuous casting of hollow bars of hot short alloys.

Clearly, apparatus correlating the speed of the pinch rolls 62 and the feed of molten material into the arbor 22 must be provided. For convenience it is not illustrated as such control apparatus is conventional.

FIG. 4 shows a modification of the air venting structure shown in FIGS. 1 and 2. In this case the venting is from above the mandrel 30 rather than from below. A tube 70 is provided extending down through the opening 26 in the arbor 22 and is connected to the bolt 32 by mechanical means such as welding at 71. In this case the bolt 32 includes a centrally located aperture 72 which communicates with the cavity 58in the mandrel 30. In operation, as the starting bar 54 lowers, air will be drawn into the cavity 58 through the tube 70 which will prevent the formation of a vacuum in the hollow 64 of the bar 66.

FIG. is similar to FIG. 4 but shows a modified vent from a tube 80 through an opening 82 in the arbor 22, an annular cavity 84 in the lower end of the arbor 22, and a passage 86 extending through the bolt 32 to the cavity 58 within the mandrel 30.

The venting structure illustrated in FIGS. 1 and 2 is the preferred embodiment because there is a greater possibility of clogging with the vents 82 or 12 in nos. 4 and s. The molten materials fed into the passage 26 in the arbor 22 are usually of temperatures of about 1200 F, or more, which is sufficient to keep the material molten under ordinary circumstances. It would not be expected that the cooler air would cause any of the molten material to congeal around the tube 70 or on the arbor adjacent to the duct 82 because of the low specific heat of air; however, it is possible, should the temperature of the molten material inadvertently be lower than anticipated.

As would be obvious to one having ordinary skill in the art, the whole molding apparatus could be tilted over on its side to provide a horizontally oriented continuous casting apparatus or a vertically upward casting apparatus as opposed to the vertically downwardly disposed apparatus as shown in FIG. 1. Such modifications are within the inventive concept disclosed herein.

FIG. 6 illustrates a modified starting plug combination 88. In this embodiment a cup-shaped element 90 is pushed upward tocontact the bottom of the mandrel 30 with the pin 92 projecting into cavity 58. Such an arrangement minimizes the possibility of melt flowing upward through the cavity 58 and into the aperture 60 through the pin. Clearly the depth of cavity 58 must be greater than the length of the pin 92 above the bottom of the plug 90.

The means 57 for locking the solidified bar 66 to the starting plug 52 illustrated in FIGS. 1-5 is preferred but other means work satisfactorily. An example of modified locking means is illustrated in FIG. 6 as tapered threads 94. This allows the workmen to disconnect the cast bar from the plug combination 88 by merely rotating the plug.

Another modified locking means is illustrated in FIGS. 7-9. Instead of the threads 94 of FIG. 6, set screws 96 are provided to project through the sidewall of cup-shaped element 90. To disconnect the plug combination 88 from the solidified bar the screws 96 are merely retracted into the sidewalls of the cup.

Several conventional ways of attaching the plug combination to the starting bar may be employed. However, the preferred way is illustrated in FIGS. 7 and 9. Slots 98 are cut in the sidewall of starting bar 54 to receive the heads of bolts 100 threaded into element 90. Such bayonet type connections are well known in the coupling art. This type of connection speeds the casting operation by allowing the workmen to quickly disengage the plug combination 88 and cast bar 66 from the starting bar 54. The cast bar can be laid aside for later use while a new starting plug combination 88 is connected to the bar 54 and the process begins anew.

I claim:

I. In a combination of a tundish for feeding molten metal to an arbor, said arbor being supported adjacent a mold and including passages for distributing the molten metal uniformly around the mandrel, said mold including l) a graphite lining and (2) a metallic jacket circumscribing said lining, said jacket including channels for the flow of cooling fluid from an inlet to an outlet, said outlet being constructed to discharge cooling fluid against the periphery of a solidified metallic shape being withdrawn from said mold,

a starting plug and bar adapted to block the mold outlet to prevent the exit of molten metal from said mold prior to its solidification at the beginning of the molding operation, and

means in contact with the starting bar and plug for controlling the rate of withdrawal of the solidified tubular metal from the mold, the improvement comprising:

the combination of the mandrel and a starting pin, said mandrel including a cavity extending from the portion nearest the mold outlet toward the arbor, the pin being fixed as part of said starting plug for projecting into said cavity and including means for locking the solidifying molten metal to the pin and plug combination when the metal solidifies within the mold,

opening means communicating with said cavity to prevent the formation of vacuum conditions within the resulting hollow of the solidified metal being withdrawn from said mold,

the spacing between the surface of the plug and the surface of the cavity being minimized to the extent that the molten'metal will not flow into the cavity and block said opening means.

2. The combination of claim 1 wherein the means for locking the solidifying molten metal to the pin and plug combination comprises a groove in the surface of the pin.

3. The combination of claim 2 wherein said groove extends completely around the circumference of the pin.

4. The combination of claim 3 wherein the surface of said starting plug in contact with molten metal is substantially planer from the pin to the mold.

5. The combination of claim 2 wherein the surface of said starting plug in contact with molten metal is substantially planer from the pin to the mold.

6. The combination of claim 1 wherein the surface of said starting plug in contact with molten metal is substantially planer from the pin to the mold.

7. The combination of claim 1 wherein the depth of the cavity is less than the length of the pin projecting above the starting plug.

8. The combination of claim 3 wherein the depth of the cavity is less than the length of the pin projecting above the starting plug.

9. The combination of claim 6 wherein the depth of the cavity is less than the length of the pin projecting above the starting plug.

10. The combination of claim 1 wherein the opening means for preventing a vacuum comprises an opening through said starting plug.

11. The combination of claim 1 wherein the opening means for preventing a vacuum comprises a passage through said mandrel.

12. The combination of claim 1 including spider means for engaging the mold and supporting the arbor adjacent said mold.

13. The combination of claim 1 wherein the starting plug includes a cup-shaped element affixed to the starting bar and a pin projecting from the bottom of said cup, said opening means comprises an aperture through said pin.

14. The combination of claim 13 wherein the means for locking the solidifying molten metal to the plug and pin combination comprises threads formed on the inside surface of the cup-shaped element.

15. The combination of claim 14 wherein the threaded surface of the cup-shaped element tapers radially inwardly from the top of the cup toward the bottom.

16. The combination of claim 13 wherein the means for locking the solidifying molten metal to the plug and pin combination comprises lug means projecting radially inwardly from the sidewall of the cup.

17. The combination of claim 16 wherein the lug means comprises retractible screws projecting through the sidewall of the cup.

18. The combination of claim 16 wherein the inner surface of said cup tapers inwardly from the top toward the bottom.

19. The combination of claim 1 wherein the starting plug is the starting bar and lugs projecting lugs projecting into the slots.

20. The combination of claim 1 wherein said graphite mold lining is lubricated by fluid applied to the exterior of the lining and permeating to the interior surface.

21. The combination of claim 1 wherein the means for controlling the rate of withdrawal of the solidified metal from the mold includes pinch rolls for contacting the starting bar and plug.

22. In a combination of a tundish to an arbor, said arbor being supported adjacent a mold and including passages for distributing the molten metal uniformly around a mandrel which is supported in the mold below said, said mandrel having a central cavity extending from its open end toward the arbor, said mold including l) a graphite lining and (2 a metallic jacket circumscribing said lipin said acket including channels for the flow of cooling fluid om an inlet to an outlet, said outlet being constructed to discharge cooling fluid against the periphery of a solidified metallic shape being withdrawn from said mold,

a starting plug and bar adapted to block the mold outlet to prevent the exit of molten metal from said mold prior to its solidification at the beginning of the molding operation, and

means in contact with the starting bar and plug for controlling the rate of withdrawal of the solidified tubular metal from the mold, the improvement comprising:

opening means communicating with said cavity to prevent the formation of vacuum conditions within the resulting hollow of the solidified metal being withdrawn from said mold,

the spacing between the surface of the plug and the surface of the cavity being minimized to the extent that the molten metal will not flow into the cavity and block said opening means,

means for locking the solidifying molten metal to the startingplug and bar when the metal solidifies within the mold.

23. The combination of claim 22 wherein the opening means for preventing a vacuum comprises an opening through said starting plug.

24. The combination of claim 22 wherein the opening means for preventing a vacuum comprises a passage through said mandrel.

25. The combination of claim 22 including spider means for engaging the mold and supporting the arbor adjacent said mold.

26. The combination of claim 22 wherein the locking means includes a pin projecting from said plug toward said mandrel, said pin including a peripheral surface of varying radius.

27. The combination of claim 22 wherein the plug comprises a cup-shaped element,

the locking means includes grooves in the interior surface of said cup-shaped element.

28. The combination of claim 22 wherein the plug comprises a cup-shaped element, V

the means for locking includes lug means projecting radially inwardly from the sidewall of the cup.

from the starting plug, said for feeding molten metal 

1. In a combination of a tundish for feeding molten metal to an arbor, said arbor being supported adjacent a mold and including passages for distributing the molten metal uniformly around the mandrel, said mold including (1) a graphite lining and (2) a metallic jacket circumscribing said lining, said jacket including channels for the flow of cooling fluid from an inlet to an outlet, said outlet being constructed to discharge cooling fluid against the periphery of a solidified metallic shape being withdrawn from said mold, a starting plug and bar adapted to block the mold outlet to prevent the exit of molten metal from said mold prior to its solidification at the beginning of the molding operation, and means in contact with the starting bar and plug for controlling the rate of withdrawal of the solidified tubular metal from the mold, the improvement comprising: the combination of the mandrel and a starting pin, said mandrel including a cavity extending from the portion nearest the mold outlet toward the arbor, the pin being fixed as part of said starting plug for projecting into said cavity and including means for locking the solidifying molten metal to the pin and plug combination when the metal solidifies within the mold, opening means communicating with said cavity to prevent the formation of vacuum conditions within the resulting hollow of the solidified metal being withdrawn from said mold, the spacing between the surface of the plug and the surface of the cavity being minimized to the extent that the molten metal will not flow into the cavity and block said opening means.
 2. The combination of claim 1 wherein the means for locking the solidifying molten metal to the pin and plug combination comprises a groove in the surface of the pin.
 3. The combination of claim 2 wherein said groove extends completely around the circumference of the pin.
 4. The combination of claim 3 wherein the surface of said starting plug in contact with molten metal is substantially planer from the pin to the mold.
 5. The combination of claim 2 wherein the surface of said starting plug in contact with molten metal is substantially planer from the pin to the mold.
 6. The combination of claim 1 wherein the surface of said starting plug in contact with molten metal is substantially planer from the pin to the mold.
 7. The combination of claim 1 wherein the depth of the cavity is less than the length of the pin projecting above the starting plug.
 8. The combination of claim 3 wherein the depth of the cavity is less than the length of the pin projecting above the starting plug.
 9. The combination of claim 6 wherein the depth of the cavity is less than the length of the pin projecting above the starting plug.
 10. The combination of claim 1 wherein the opening means for preventing a vacuum comprises an opening through said starting plug.
 11. The combination of claim 1 wherein the opening means for preventing a vacuum comprises a passage through said mandrel.
 12. The combination of claim 1 including spider means for engaging the mold and supporting the arbor adjacent said mold.
 13. The combination of claim 1 wherein the starting plug includes a cup-shaped element affixed to the starting bar and a pin projecting from the bottom of said cup, said opening means comprises an aperture through said pin.
 14. The combination of claim 13 wherein the means for locking the solidifying molten metal to the plug and pin combination comprises threads formed on the inside surface of the cup-shaped element.
 15. The combination of claim 14 wherein the threaded surface of the cup-shaped element tapers radially inwardly from the top of the cup toward the bottom.
 16. The combination of claim 13 wherein the means for locking the solidifying molten metal to the plug and pin combination coMprises lug means projecting radially inwardly from the sidewall of the cup.
 17. The combination of claim 16 wherein the lug means comprises retractible screws projecting through the sidewall of the cup.
 18. The combination of claim 16 wherein the inner surface of said cup tapers inwardly from the top toward the bottom.
 19. The combination of claim 1 wherein the starting plug is secured to the starting bar by slots formed in the sidewall of the starting bar and lugs projecting from the starting plug, said lugs projecting into the slots.
 20. The combination of claim 1 wherein said graphite mold lining is lubricated by fluid applied to the exterior of the lining and permeating to the interior surface.
 21. The combination of claim 1 wherein the means for controlling the rate of withdrawal of the solidified metal from the mold includes pinch rolls for contacting the starting bar and plug.
 22. In a combination of a tundish for feeding molten metal to an arbor, said arbor being supported adjacent a mold and including passages for distributing the molten metal uniformly around a mandrel which is supported in the mold below said, said mandrel having a central cavity extending from its open end toward the arbor, said mold including (1) a graphite lining and (2) a metallic jacket circumscribing said lining, said jacket including channels for the flow of cooling fluid from an inlet to an outlet, said outlet being constructed to discharge cooling fluid against the periphery of a solidified metallic shape being withdrawn from said mold, a starting plug and bar adapted to block the mold outlet to prevent the exit of molten metal from said mold prior to its solidification at the beginning of the molding operation, and means in contact with the starting bar and plug for controlling the rate of withdrawal of the solidified tubular metal from the mold, the improvement comprising: opening means communicating with said cavity to prevent the formation of vacuum conditions within the resulting hollow of the solidified metal being withdrawn from said mold, the spacing between the surface of the plug and the surface of the cavity being minimized to the extent that the molten metal will not flow into the cavity and block said opening means, means for locking the solidifying molten metal to the starting plug and bar when the metal solidifies within the mold.
 23. The combination of claim 22 wherein the opening means for preventing a vacuum comprises an opening through said starting plug.
 24. The combination of claim 22 wherein the opening means for preventing a vacuum comprises a passage through said mandrel.
 25. The combination of claim 22 including spider means for engaging the mold and supporting the arbor adjacent said mold.
 26. The combination of claim 22 wherein the locking means includes a pin projecting from said plug toward said mandrel, said pin including a peripheral surface of varying radius.
 27. The combination of claim 22 wherein the plug comprises a cup-shaped element, the locking means includes grooves in the interior surface of said cup-shaped element.
 28. The combination of claim 22 wherein the plug comprises a cup-shaped element, the means for locking includes lug means projecting radially inwardly from the sidewall of the cup. 